Gas generating composition

ABSTRACT

Provided is a gas generating composition which easily generates a lumpy combustion residue and has good ignition ability. The gas generating composition includes a fuel and an oxidizing agent and meets the following requirements (a), (b), and (c):
         (a) one or more metals selected from copper, silver, platinum, and gold are included in the composition;   (b) the combustion residue of the composition is formed substantially by one or more metals selected from copper, silver, platinum, and gold; and   (c) the combustion temperature of the composition is less than a temperature obtained by adding 200° C. to the melting point of copper, silver, platinum, or gold contained therein.

TECHNICAL FIELD

The present invention relates to a gas generating composition that can be used in a gas generator for an airbag apparatus.

BACKGROUND ART

A coolant/filter is used in gas generators to decrease temperature of combustion gas and filter combustion residues, but since the mass ratio of the coolant/filter in the entire gas generator is large, it is demanded to reduce the coolant/filter in weight.

When the combustion temperature of a gas generating agent used in the gas generator is decreased, a thermal load on the coolant/filter can be reduced. Therefore, the usage amount (mass) of the coolant/filter can be reduced and the weight of the entire gas generator can be decreased.

JP-A No. H09-328389 discloses a composition including guanidine nitrate and basic copper nitrate described in the Examples.

In JP-A No. 2001-220282, since a metal oxide is generated as a combustion residue, the aggregation of the combustion residue can be inhibited by itself and the residue formed by fine particles is generated.

In WO-A No. 03/016244, the combustion temperature is sufficiently lowered and the coolant/filter can be reduced in weight.

SUMMARY OF THE INVENTION

As a means for resolving the aforementioned problem, the present invention provides a gas generating composition including a fuel and an oxidizing agent, the composition meeting the following requirements (a), (b), and (c):

(a) one or more metals selected from copper, silver, platinum, and gold is included in the composition;

(b) the combustion residue of the composition is formed substantially by one or more metals selected from copper, silver, platinum, and gold; and

(c) the combustion temperature of the composition is less than a temperature obtained by adding 200° C. to the melting point of copper, silver, platinum, or gold contained therein.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus are not limitative of the present invention and wherein:

FIG. 1 is a photo illustrating the state of the residue after the residue aggregation test using the composition of Example 4; and

FIG. 2 is a photo illustrating the state of the residue after the residue aggregation test using the composition of Comparative Example 1.

DETAILED DESCRIPTION OF THE INVENTION

In JP-A No. H09-328389, the combustion temperature is not sufficiently reduced. Therefore, in the case of being used in a gas generator, the coolant/filter is difficult to reduce in weight.

In JP-A No. 2001-220282, a filter with small apertures is required. Therefore, in the case of being used in a gas generator, the coolant/filter is difficult to reduce in weight.

In WO-A No. 03/016244, there is a room for improvement in terms of ignition ability.

The present invention is to provide a gas generating composition that reduces the combustion temperature and increase the filtering ability of a coolant/filter by producing a lumpy combustion residue, without pulverizing.

The gas generating composition of the present invention easily forms a lumpy combustion residue, has a low combustion temperature, and also demonstrates good ignition ability.

DETAILED DESCRIPTION OF INVENTION

One, or two or more listed hereinbelow can be used as a fuel included in the gas generating composition of the present invention:

guanidine nitrate, aminoguanidine nitrate, nitroguanidine, triaminoguanidine nitrate;

a triazine compound such as melamine, cyanuric acid, melamine cyanurate, ammeline, and ammelide;

a nitroamine compound such as trimethylene trinitroamine (RDX), cyclotetramethylene tetranitramine (HMX), azodicarbonamide (ADCA), and dicyandiamide (DCDA);

a tetrazole derivative such as 5-aminotetrazole (5-AT) and a 5-aminotetrazole metal salt; and

a bitetrazole derivative such as bitetrazole, a bitetrazole metal salt, and bitetrazole ammonium salt.

It is preferred that the fuel included in the gas generating composition of the present invention be formed by a combination of a first fuel component and a second fuel component.

It is also preferred that the combustion temperature could be decreased by including the first fuel component and that the ignition ability be increased by including the second fuel component.

Examples of the first fuel component include aminoguanidine nitrate, triaminoguanidine nitrate, and triazine compounds such as melamine, cyanuric acid, melamine cyanurate, ammeline, and ammelide.

Examples of the second fuel component include nitroguanidine, trimethylene trinitroamine (RDX), cyclotetramethylene tetranitramine (HMX), azodicarbonamide (ADCA), dicyandiamide (DCDA), a tetrazole derivative such as 5-aminotetrazole (5-AT) and a 5-aminotetrazole metal salt, a bitetrazole derivative such as bitetrazole, a bitetrazole metal salt, and bitetrazole ammonium salt.

One or more selected from melamine, melamine cyanurate, and guanidine nitrate are preferred as the first fuel component.

One or more selected from nitroguanidine and 5-aminotetrazole are preferred as the second fuel component.

In accordance with the present invention, it is especially preferred that melamine cyanurate be included as the first fuel component and nitroguanidine be included as the second fuel component.

In accordance with the present invention, it is also especially preferred that guanidine nitrate be included as the first fuel component and nitroguanidine be included as the second fuel component.

In order to decrease the combustion temperature and improve the ignition ability, it is preferred that the fuel include the first fuel component and second fuel component at the following ratios:

The content ratio of the first fuel component is preferably 0 to 40% by mass, more preferably 3 to 25% by mass, and even more preferably 5 to 10% by mass; and

The content ratio of the second fuel component is preferably 0 to 40% by mass, more preferably 3 to 30% by mass, and even more preferably 10 to 28% by mass.

A known oxidizing agent can be used as an oxidizing agent in the gas generating composition of the present invention, but in order to meet the requirement (a), it is preferred that a compound including copper, silver, platinum, or gold be used.

An oxidizing agent including copper is preferred, and it is more preferred that the oxidizing agent be selected from basic copper nitrate and basic copper carbonate. It is even more preferred that basic copper nitrate and basic copper carbonate be used in combination with each other.

When the oxidizing agent selected from basic copper nitrate and basic copper carbonate is used, the content ratio thereof in the composition is preferably 20 to 80% by mass, more preferably 50 to 75% by mass.

When basic copper nitrate and basic copper carbonate are used together, the content ratio of basic copper nitrate in the total amount is preferably 1 to 70% by mass, more preferably 25 to 65% by mass, and the ratio of basic copper carbonate is preferably 1 to 50% by mass, more preferably 3 to 30% by mass.

The gas generating composition of the present invention includes the above-described fuel and oxidizing agent and meets the below-described requirements (a), (b), and (c).

Where known aluminum hydroxide is compounded as a cooling agent in the gas generating composition, the combustion temperature can be reduced, but because the combustion residue is pulverized, it is necessary to increase a density of the coolant/filter in order to increase the filtering ability, and the coolant/filter cannot be reduced in weight.

The gas generating composition of the present invention resolves this problem by including the above-described fuel and oxidizing agent and meeting the following requirements (a), (b), and (c).

<Requirement (a)>

One or more metals selected from copper, silver, platinum, and gold are included in the composition.

The above-mentioned metals are contained as compounds thereof, but may be also included as simple metals.

The gas generating composition includes a binder and various additives in addition to the fuel and the oxidizing agent, and compositions in which various metals are included in those components can be used.

Metals with a smaller ionization tendency such as copper, silver, platinum, and gold easier remain as simple metals in the combustion residue and easier generate lumpy residues. Therefore, they can be easily filtered with a coolant/filter, and a coolant/filter with a large mesh size (small density) can be used, thereby making it possible to reduce weight.

Conversely, where the ionization tendency increases, finely powdered metal oxides are easily formed after the combustion, a coolant/filter with a smaller mesh size (higher density) should be used for filtering, and the weight cannot be reduced.

Metals with a standard electrode potential higher/lower than 0.00 V, which is the standard electrode potential of hydrogen and taken as a reference, are assumed to have a small/large ionization tendency.

In the requirement (a), the content of one or more metals selected from copper, silver, platinum, and gold in all of the metals in the composition is preferably not less than 92% by mass, or 92 to 100% by mass, more preferably 95 to 100% by mass, even more preferably 95 to 99% by mass.

The content of the metal in all of the metals in the composition, as referred to herein, is determined by theoretical computations from the gas generating composition used.

<Requirement (b)>

The combustion residue of the composition is formed substantially by one or more metals selected from copper, silver, platinum, and gold.

The expression “the combustion residue is formed substantially by one or more metals selected from copper, silver, platinum, and gold” used herein means that the content of the metal component in the combustion residue is 90 to 100% by mass, preferably 93 to 100% by mass, more preferably 93 to 99% by mass. A metal oxide or a metal compound including the metal may be included as a balance.

The content of the metal component in the combustion residue, as referred to herein, is theoretically computed from the gas generating composition used. Where the requirement (b) is met, the aggregation of the metal induced by metal oxide is not inhibited and, therefore, a lumpy combustion residue is easily formed.

<Requirement (c)>

The combustion temperature of the composition is less than a temperature obtained by adding 200° C. to the melting point of copper, silver, platinum, or gold contained therein. Thus, the combustion temperature is less than a value obtained by adding 200° C. to the value of the melting point (° C.) of copper, silver, platinum, or gold.

Where the requirement (c) is met, the combustion residue easily becomes lumpy.

The composition in accordance with the present invention can also include a binder and known additives serving to adjust the burning rate of the gas generating composition and purify the combustion gas, provided that the requirements (a), (b), and (c) are met and the purpose of the present invention can be attained.

It is preferred that the composition in accordance with the present invention meet the requirements (a), (b), and (c) by using copper. Thus, in the requirement (a), it is preferred that the composition include copper.

The binder can be one or two or more selected from carboxymethyl cellulose (CMC), carboxymethyl cellulose sodium salt (CMCNa), carboxymethyl cellulose potassium salt, carboxymethyl cellulose ammonium salt, cellulose acetate, cellulose acetate butyrate (CAB), ethyl cellulose (EC), hydroxyethyl cellulose (HEC), microcrystalline cellulose, polyacryl hydrazide, a copolymer of acrylamide and a metal salt of acrylic acid, a copolymer of polyacrylamide and a polyacrylic acid ester compound, acrylic rubber, and silicone.

Known additives can include metal oxides such as copper (II) oxide, iron oxide, zinc oxide, cobalt oxide, manganese oxide, molybdenum oxide, nickel oxide, bismuth oxide, silica, and alumina; cobalt carbonate, calcium carbonate; complex compounds of metal oxides or hydroxides such as Japanese acid clay, kaolin, talc, bentonite, diatomaceous earth, and hydrotalcite; metal acid salts such as sodium silicate, mica molybdate, cobalt molybdate, and ammonium molybdate; molybdenum disulfide, calcium stearate, silicon nitride, silicon carbide, metaboric acid, boric acid, and anhydrous boric acid, provided that they do not inhibit the aggregation of the combustion residue including metal.

The gas generating composition in accordance with the present invention can be molded to the desired shape, and can be in the form of a molded article of a single-perforated columnar shape, a perforated (porous) columnar shape, or a pellet. The molded article can be manufactured by adding water or an organic solvent to the gas generating composition, mixing and extrusion-molding (a molded article in the form of a cylinder having a single hole or a perforated (porous) cylinder), or by compression-molding with a pelletizer or the like (a molded article in a shape of a pellet).

The gas generating composition in accordance with the present invention and a molded article obtained therefrom can be used, for example, in an airbag inflator of a driver seat, an airbag inflator of a passenger seat next to the driver, a side airbag inflator, an inflator for an inflatable curtain, an inflator for a knee bolster, an inflator for an inflatable seat belt, an inflator for a tubular system, and an inflator for a pretensioner, of various vehicles.

The inflator using the gas generating composition in accordance with the present invention or a molded article obtained therefrom may be of a pyrotechnic type in which a gas supplying source is only a gas generating agent and of a hybrid type which uses both a compressed gas such as argon and a gas generating agent.

The gas generating composition in accordance with the present invention or a molded article obtained therefrom can be also used as an igniting agent called an enhancer (or a booster) or the like, serving to transmit the energy of a detonator or a squib to the gas generating agent

EXAMPLES Example 1

Molded articles made of the gas generating compositions including the components indicated in Table 1 were manufactured. The properties indicated in Table 1 were measured with respect to the compositions. The results are shown in Table 1.

(1) Residue Aggregation Ability

◯: a lumpy shape can be visually recognized; the lumps do not collapse when pinched between the fingers;

X: a powder shape is visually recognized, or though a lumpy shape can be visually recognized, the lumps are crushed into a powder when pinched between the fingers.

(2) Combustion Temperature (K)

A combustion temperature based on theoretical computations.

(3) Pressure Index

A pressure index was determined by measuring the burning rate by the following method.

(Method for Preparing a Round Columnar Strand).

The molded articles of the compositions of the examples and the comparative examples were pulverized in a mortar, and a powder that has passed through a metal net with a mesh size of 500 μm was loaded into a receiving die of a predetermined die.

The powder was then compressed under a pressure of 21.78 KN by using a hydraulic pump from the pestle end surface, held for 5 seconds in the compressed state, then taken out, and molded under a surface pressure of 30.42 KN/cm² into a round columnar strand with an outer diameter of 9.55 mm and a length of 12.70 mm.

The obtained round columnar molded article was dried for 16 hours at 110° C. An epoxy resin adhesive (“Bond Quick 30”, produced by Konishi Co., Ltd.) was then coated on the side surface of the round columnar molded article and cured. A sample that is ignited only from the end surface and is not ignited from the side surface was thus obtained.

(Method for Measuring the Burning Rate)

The round columnar strand serving as a sample was disposed in a SUS sealed cylinder with an internal volume of 1 liter, the cylinder interior was entirely purged with nitrogen, and the pressure inside thereof was then raised to and stabilized at 6860 kPa. A predetermined electric current was then allowed to flow to a nichrome wire that was brought into contact with the end surface of the strand and the strand was ignited and combusted by the meltdown energy thereof.

Changes in pressure inside the cylinder with time were verified with a recorder chart, the time elapsed from the start of combustion to the peak of pressure increase was verified from the chart memory, and the numerical value obtained by dividing the strand length before the combustion by the elapsed time was taken as the burning rate.

The tests in which the pressure was increased to and stabilized at 4900 kPa and 8820 kPa were conducted in the same manner as described hereinabove.

(Pressure Index)

The burning rate under a nitrogen atmosphere was measured under a pressure of 4900, 6860, and 8820 kPa by using the round columnar strands manufactured by the above-described method.

In the Examples, the pressure index within a range of 4900 kPa to 8820 kPa is shown.

TABLE 1 Content Gas generating composition of copper Content Combus- in solid of copper Residue tion residue in entire aggre- temper- Oxygen Pres- compo- Japanese metal gation ature balance sure nent MC GN NQ BCN BCC SrN CMCNa Al(OH)₃ Acid Clay (wt %) ability (K) (g/g) index (wt %) Example 14.4 11.4 64.2 5.0 5.0 99.1 ∘ 1522 −0.007 0.10 97.3 1 Example 1.4 26.9 26.7 40.0 5.0 98.0 ∘ 1518 −0.007 0.10 97.3 2 Example 8.1 22.4 41.5 25.0 3.0 99.2 ∘ 1545 −0.007 0.10 98.4 3 Example 6.0 17.9 44.2 25.0 7.0 98.3 ∘ 1490 −0.007 0.10 96.4 4 Example 7.8 17.5 44.7 25.0 5.0 98.8 ∘ 1495 0.000 0.10 97.0 5 Example 5.4 25.4 39.2 25.0 5.0 98.6 ∘ 1565 −0.020 0.10 97.2 6 Example 19.6 13.0 28.4 34.0 5.0 98.1 ∘ 1523 −0.007 — 96.6 7 Example 34.8 1.0 33.2 26.0 5.0 98.4 ∘ 1532 −0.007 — 97.0 8 Example 0.6 28.0 22.4 44.0 5.0 97.6 ∘ 1512 −0.007 — 97.3 9 Example 26.4 11.0 25.6 34.0 3.0 98.7 ∘ 1542 −0.007 — 98.2 10 Example 12.8 15.0 31.2 34.0 7.0 97.6 ∘ 1503 −0.007 — 96.2 11 Example 23.9 7.9 29.2 34.0 5.0 98.1 ∘ 1502 0.000 — 97.2 12 Example 11.6 22.5 26.9 34.0 5.0 98.0 ∘ 1562 −0.020 — 97.1 13 Compara- 40.7 49.3 5.0 5.0 94.7 x 1700 −0.009 0.30 85.9 tive Ex. 1 Compara- 38.0 47.0 5.0 10.0 90.5 x 1582 −0.009 — 76.7 tive Ex. 2 Compara- 35.4 44.6 5.0 15.0 86.3 x 1462 −0.009 — 68.6 tive Ex. 3 Compara- 34.4 49.5 9.4 6.7 0.0 x 2410 −0.013 0.60 0.0 tive Ex. 4 Compara- 33.8 55.2 10.0 1.0 0.0 x 2460 0.004 0.60 0.0 tive Ex. 5 Compara- 52.1 47.9 100.0 x 1889 0.007 — 75.7 tive Ex. 6

Examples 1 to 13 meet the requirements (a), (b), and (c). As a result, a lumpy combustion residue was easily formed, the combustion temperature was low, and good ignition ability was demonstrated. The combustion residue of Example 4 was lumpy as depicted in FIG. 1 and did not collapse when pinched between the fingers. The same result was obtained in the other Examples.

None of Comparative Examples 1 to 6 meet the requirements (a), (b), and (c). As a result, the combustion residue was in the form of a fine powder, the combustion temperature was high, and the pressure index was also high. In Comparative Example 3, the combustion temperature was low because aluminum hydroxide was included.

The combustion residue in Comparative Example 5 was in the form of a powder. The combustion residue in Comparative Example 1 was in the form of lumps, but the lumps were readily crushed into a powder when pinched between the fingers (see FIG. 2).

The invention thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims. 

1. A gas generating composition comprising a fuel and an oxidizing agent, the composition meeting the following requirements (a), (b), and (c): (a) at least one metal selected from the croup consisting of copper, silver, platinum, and gold is included in the composition; (b) the combustion residue of the composition is formed substantially by at least one metal selected from the group consisting of copper, silver, platinum, and gold; and (c) the combustion temperature of the composition is less than a temperature obtained by adding 200° C. to the melting point of copper, silver, platinum, or gold contained therein.
 2. The gas generating composition according to claim 1, wherein the fuel is at least one selected from the group consisting of guanidine nitrate, aminoguanidine nitrate, nitroguanidine, triaminoguanidine nitrate, melamine, cyanuric acid, melamine cyanurate, ammeline, ammelide, trimethylene trinitroamine (RDX), cyclotetramethylene tetranitramine (HMX), azodicarbonamide (ADCA), dicyandiamide (DCDA), 5-aminotetrazole (5-AT), 5-aminotetrazole metal salt, bitetrazole, a bitetrazole metal salt, and bitetrazole ammonium salt.
 3. The gas generating composition according to claim 1, wherein the fuel is made of a combination of a first fuel component of at least one selected from the group consisting of melamine, melamine cyanurate, and guanidine nitrate, and a second fuel component of at least one selected from the group consisting of nitroguanidine and 5-aminotetrazole.
 4. The gas generating composition according to claim 1, wherein the content of at least one metal selected from the group consisting of copper, silver, platinum, and gold in all of the metals in the composition in the requirement (a) is not less than 92% by mass.
 5. The gas generating composition according to claim 1, wherein melamine cyanurate is included as the first fuel component and nitroguanidine is included as the second fuel component in the fuel.
 6. The gas generating composition according to claim 1, wherein guanidine nitrate is included as the first fuel component and nitroguanidine is included as the second fuel component in the fuel. 